Valgrind BBV, Быстрый старт

Страница: 17 / 319

Using and understanding the Valgrind core
You can direct the commentary to three different places:
1. The default: send it to a file descriptor, which is by default 2 (stderr). So, if you give the core no options, it will
write commentary to the standard error stream. If you want to send it to some other file descriptor, for example
number 9, you can specify
--log-fd=9
.
This is the simplest and most common arrangement, but can cause problems when Valgrinding entire trees of
processes which expect specific file descriptors, particularly stdin/stdout/stderr, to be available for their own use.
2. A less intrusive option is to write the commentary to a file, which you specify by
--log-file=filename
.
There are special format specifiers that can be used to use a process ID or an environment variable name in the log
file name. These are useful/necessary if your program invokes multiple processes (especially for MPI programs).
See the
basic options section for more details.
3. The least intrusive option is to send the commentary to a network socket. The socket is specified as an IP address
and port number pair, like this:
--log-socket=192.168.0.1:12345
if you want to send the output to host
IP 192.168.0.1 port 12345 (note: we have no idea if 12345 is a port of pre-existing significance). You can also omit
the port number:
--log-socket=192.168.0.1 , in which case a default port of 1500 is used. This default is
defined by the constant VG_CLO_DEFAULT_LOGPORT in the sources.
Note, unfortunately, that you have to use an IP address here, rather than a hostname.
Writing to a network socket is pointless if you don’t have something listening at the other end. We provide a simple
listener program,
valgrind-listener
, which accepts connections on the specified port and copies whatever
it is sent to stdout. Probably someone will tell us this is a horrible security risk. It seems likely that people will
write more sophisticated listeners in the fullness of time.
valgrind-listener
can accept simultaneous connections from up to 50 Valgrinded processes. In front of
each line of output it prints the current number of active connections in round brackets.
valgrind-listener
accepts two command-line options:
• -e or --exit-at-zero : when the number of connected processes falls back to zero, exit. Without this, it
will run forever, that is, until you send it Control-C.
• portnumber : changes the port it listens on from the default (1500). The specified port must be in the range
1024 to 65535. The same restriction applies to port numbers specified by a
--log-socket
to Valgrind itself.
If a Valgrinded process fails to connect to a listener, for whatever reason (the listener isn’t running, invalid or
unreachable host or port, etc), Valgrind switches back to writing the commentary to stderr.
The same goes for
any process which loses an established connection to a listener. In other words, killing the listener doesn’t kill the
processes sending data to it.
5